macOS Catalina 10.15.4 breakage

[Jonathan Perkin <jperkin%joyent.com@localhost>]

I upgraded my macos15 bulk build hosts today to 10.15.4, and now
bootstrap is failing where previously it was fine with 10.15.3.

The errors are all similarly related to dyld, for example:

  dyld: dyld cache load error: shared cache file open() failed
  dyld: Symbol not found: _xmlFree
    Referenced from: /usr/lib/libxar.1.dylib
    Expected in: /usr/lib/libxar.1.dylib
  in /usr/lib/libxar.1.dylib
  clang: error: unable to execute command: Abort trap: 6
  clang: error: linker command failed due to signal (use -v to see invocation)

or:

  dyld: dyld cache load error: shared cache file open() failed
  dyld: Symbol not found: ___gxx_personality_v0
    Referenced from: /usr/lib/libobjc.A.dylib
    Expected in: /usr/lib/libobjc.A.dylib
  in /usr/lib/libobjc.A.dylib
  bmake: "../../mk/buildlink3/../../mk/buildlink3/find-libs.mk" line 65: warning: "if test "`echo /usr/lib/libssl.*`" != "/usr/lib/libssl.*"; then  echo yes;						 else								 echo no;						 fi" exited on a signal

I think it's something to do with the sandbox builds, as I can't
reproduce this just by running e.g. clang outside.  Then again if I
create a temporary sandbox I can't reproduce it either.

Anyone else seeing similar issues, or know what might have changed in
.4 to cause this?  I'm going to play around with the various
DYLD_SHARED_CACHE_* settings to see if I can get things working again.

Thanks,

-- 
Jonathan Perkin  -  Joyent, Inc.  -  www.joyent.com